Scrambling of speech signal with high security - method based on voiced and voiceless parts of speech

摘要

Voiced sounds take the form of damped oscillations. The voiced parts are divided into time slots based on the period of these oscillations. Voiceless sounds have no relationship between the speech signal and the slot period. They have a fixed middle frequency. To reduce the transmission bandwidth only every n-th slot is used. The signals are stored and the slots to be transmitted may be selected before or after storage. The signal in only certain irregularly chosen slots is transmitted. The time slots are then taken in groups. Parts of some groups include no information. Where this is the case, the information is read out of the store at a reduced rate governed by the empty slots available so that the information fills out the time available. Degree of scrambling is increased by reverse reading out of information.